1. Field
The current disclosure relates to small form-factor pluggable (SFP) transceivers, and more specifically but not exclusively, to SFP transceivers used for connecting client-premises equipment to an optical data network.
2. Description of the Related Art
Optical data networks are used to provide high-speed and high-throughput data communication to clients. The backbone of an optical data network uses optical fibers, which carry light, to transmit data among network hubs and central offices of an optical-network provider's access network. The optical-network backbone connects to a client's premises via a metropolitan-access segment that uses a fiber optic cable from a proximate central office. The network segment from the central office to the client's premises is sometimes referred to as the first mile (as viewed from the client's perspective) or the last mile (as viewed from the provider's perspective)—although the actual distance typically ranges from dozens of meters up to a few dozen kilometers.
At the client premises, the optical fiber connects to a network interface device (NID) that (i) demarcates the boundary between the provider's access network—which is the provider's responsibility—and the client's local network—which is the client's responsibility—and (ii) provides interconnectivity and translation, as needed, between the provider's optical network and the client's optical equipment. In other words, a typical NID connects from a first type optical network suitable for medium-distance transmission to a second type optical network suitable for short-distance transmission. Note that (i) a NID is also known as a demarcation device and (ii) an access network is also known as a transport network. Note further that, in some fiber-optic network setups, one entity—a network provider—manages the physical fiber-optic network while a separate entity—a service provider—provides optical data services over that network to clients such as end users. In the latter type of setups, additional network devices might be required at the client premises because of the plurality of parties involved in the provision and use of the network services.
The logical processing performed internally by a NID is done electronically—as opposed to optically—using integrated circuit (IC) chips. Consequently, the NID performs optical-to-electrical (o/e) and electrical-to-optical (e/o) signal conversions in order to perform electronic processing while receiving and transmitting optical signals. These conversions are typically performed by SFP transceivers, which—as their name suggests—are small, pluggable devices that connect to an optical cable at a first connective interface and plug into corresponding receptacles, sometimes called cages, of an electronic device—such as a NID—connecting at a second connective interface. Industry-wide specifications for SFP transceivers are determined and provided by the SFF (Small Form Factor) Committee, an ad-hoc group of electronics industry participants. One such standard for SFP transceivers is INF-8074i (available at ftp://ftp.seagate.com/sff/INF-8074.PDF), incorporated herein by reference in its entirety.
FIG. 1 shows a simplified functional diagram of conventional SFP transceiver 100. SFP transceiver 100 comprises optical transceiver 101, controller 102, EEPROM (electronically erasable programmable read-only memory) 104, and electrical connector 103. Optical transceiver 101 connects to fiber optic cable 100a, which typically—in networking applications—includes two optical fibers, namely, a transmit fiber and a receive fiber. Note that, in some setups, fiber optic cable 100a includes only one optical fiber, which may be used to transmit and/or receive data. Fiber optic cable 100a may also be generically referred to as an optical link. Optical transceiver 101 converts (i) electrical signals provided by controller 102 and/or electrical connector 103 (via controller 102) into optical signals for provision to the transmit fiber of fiber-optic cable 100a and (ii) optical signals received from the receive fiber of fiber-optic cable 100a into electrical signals for provision to controller 102 and/or electrical connector 103. SFP transceiver is sometimes referred to as an optical network unit (ONU) because of its optical/electrical conversions.
Optical transceiver 101 connects to controller 102 via path 102a. Connector 103 connects to controller 102 via path 102b. Connector 103 is adapted to plug into a corresponding connector of a host electronic device (not shown) and communicate via signal path 100b. Controller 102 provides basic control functions for the operation of SFP transceiver 100 and interconnects the internal components of SFP transceiver 100. EEPROM 104, which is connected to controller 102 via path 104a, stores inventory data such as, for example, model name and serial number. The host typically comprises a serializer/deserializer (SerDes) for the conversion of parallel signals on the user-equipment side to/from serial signals used on the service-provider side. Path 100b also provides electrical power to SFP transceiver 100.
FIG. 2 shows typical optical-network segment 200 that includes central office (CO) node 201 connected to client device 202, having an optical interface and located at client site 203. Central office node 201—also known as a metro node—connects to NID 204—located at client site 203—via optical path 201a. NID 204 is a device provided, operated, and maintained by the service provider and, in addition to the NID functions described above, is used by the service provider to set up, monitor, and troubleshoot the connection from CO node 201 to client site 203. These operations may include (1) service activation, (2) operations, administration, and maintenance (OAM), (3) Quality of Service (QoS) management, (4) virtual local area network (VLAN) processing, and (5) synchronization distribution. OAM functions are used by the service provider to monitor service, troubleshoot problems, and localize faults, as well as measure performance to verify conformance to the service-level agreement (SLA) between the service provider and the client.
NID 204 is powered via a connection to a regular electrical power socket. Since the internal processing performed by NID 204 is performed electronically while communication to CO node 201 and client device 202 is performed optically, NID 204 uses two SFP transceivers, namely, SFP transceivers 205 and 206, which are substantially similar to SFP transceiver 100 of FIG. 1. SFP transceivers 205 and 206 are plugged into corresponding receptacles in NID 204. Note that an SFP-transceiver receptacle, such as the receptacles of NID 204, includes an electrical connector which makes direct physical contact with the electrical connector of the corresponding SFP transceiver when the SFP transceiver is plugged into the receptacle. SFP transceiver 205 connects, via optical fiber 201a, to CO node 201 and SFP transceiver 206 connects, via optical fiber 204a, to client device 202. NID 204 may include LEDs corresponding to SFP transceivers 205 and 206, which indicate, for example, whether the corresponding link is up or down, based on a determination made by NID 204.
The demarcation between the provider's network and the client's network is represented in FIG. 2 by dotted line 207. The physical port or interface that forms the boundary between the two networks is known as a user-network interface (UNI). The part of the network provider's equipment that performs and controls the UNI is sometimes designated as UNI-N while the part of the customer's equipment that performs UNI functions is sometimes designated as UNI-C. Standard features for UNIs are defined by the Metro Ethernet Forum (MEF). In network segment 200, the UNI would be where SFP transceiver 206 connects to optical cable 204a since optical cable 204a is the client's responsibility—as are SFP transceiver 208 and client device 202—while SFP transceiver 206 is the network provider's responsibility—as are NID 204, SFP transceiver 205, and optical cable 201a. Using SFP transceiver 206 and optical cable 204a, NID 204 provides an optical connection to client device 202. Client device 202 uses SFP transceiver 208, also similar to SFP transceiver 100 of FIG. 1, to connect to local optical fiber 204a and convert between optical and electrical signals. Client device 202 may be, for example, a network router connected to the client's local area network.